In silico investigations into lysosomal arrhythmia causation

Thesis

During intracellular calcium overload, ryanodine receptors (RyRs) spontaneously release calcium, which can result in delayed afterdepolarizations that are strongly linked to potentially fatal arrhythmias. The sarcoplasmic reticulum acts as the primary calcium store in cardiomyocytes. Other organelles, such as mitochondria and lysosomes, may also act as calcium stores. Type 2 two-pore channels (TPC2) are principally responsible for releasing lysosomal calcium upon activation by NAADP. It has been demonstrated that knockout of two-pore channel 2 (TPC2) inhibits lysosomal calcium release, which decreases the occurrence of ventricular arrhythmias during β-adrenergic stimulation. There are currently no mechanistic studies examining how lysosomal function affects RyR spontaneous release. In this thesis, I study how lysosome function affects calcium loading, which in turn influences RyR spontaneous release. This allows us to understand how lysosomes might mediate arrhythmias. Understanding the role of lysosomal calcium as a potential contributor to the generation of arrhythmias can be approached by alternative approaches to controlled wet-lab experimentation, which restrain variability experimentally and statistically. Mechanistic investigations were conducted using a population of biophysically detailed mouse ventricular and human atrial cardiomyocyte models including lysosome calcium handling and incorporating variability, and calibrated by experimental findings. Here I demonstrate that lysosomal calcium uptake and release can synergistically form a pathway for fast calcium transport, by which lysosomal calcium release primarily modulates sarcoplasmic reticulum calcium ATPase reuptake and RyR release. Enhancing this pathway contributes to pro-arrhythmias. Notably, blocking this pathway revealed an antiarrhythmic impact on the cell. In ventricular cardiomyocytes, lysosomal calcium handling promotes RyR spontaneous release by elevating RyR open probability. In atrial cardiomyocytes, lysosomal release promotes early afterdepolarisations by increasing sodium calcium exchange inward current and late L-type calcium current. When considered collectively, the studies show that proarrhythmic mediators are directly influenced by lysosomal calcium handling, indicating potential antiarrhythmic approaches and revealing important modulators of lysosomal proarrhythmic action.

Authors: Meng, Z

• DOI: 10.5287/ora-d5zbjz8m2
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: calcium; TPC; lysosome; NAADP; modelling; arrhythmia
• Subjects: Programming by example (Computer science); Physiology; Pharmacology